1. Field of the Invention
This invention relates generally to containers and methods for delivering liquid chemicals to a point of use. Mores specifically, to containers and methods wherein a gaseous media is used to push the liquid chemical out of the container.
2. Related Art
In certain chemical processes, such as chemical vapor deposition with organometallic precursors (MOCVD), there is often the need to pressurize supply reagent containers with inert gas in order to provide sufficient pressure in the container to deliver the chemical to the chemical vapor deposition tool. The vapor pressure of the liquid chemical at use temperature alone is frequently not sufficient to deliver the chemical to the chemical vapor deposition tool. Heating the chemical to raise its vapor pressure in these cases is not practical and often leads to premature degradation of the precursor chemical. Mechanical pumps may also lead to contamination.
It is known practice to introduce inert gas under pressure into a container in order to force chemical out of the container and down a process line. Indeed, certain suppliers advertise integral internal filters for gas delivery cylinders. However, unlike other applications, in MOCVD, the precursor such as pentaethoxy tantalum, zirconium t-butoxide, titanium tetrachloride, and the like, are extremely reactive to air contaminants, particularly moisture, to form metal oxide solids and various other hazardous materials (depending on the compound) often along with large releases of energy. For this reason, even minute traces of air contaminants cannot be tolerated in delivery equipment for such precursor chemicals. Furthermore, there is need to periodically change out supply containers as chemicals are consumed during processing of semiconductors. It is mainly in the change-out of containers where there is greatest potential to contaminate the delivery system and therefore the precursor chemical. For this reason good purge out sequences for delivery systems are required to be carried out as stipulated by semiconductor equipment manufacturers.
The need for good purging techniques are required for all air-sensitive compounds, even those with high vapor pressure precursors. However, in the case of low vapor pressure chemicals, the air contaminant issue is much more severe because such contaminants are introduced into the container and hence contaminate the entire container of product after which these contaminants cannot be simply flushed out using a purging manifold. Such contamination can be quite costly to the user since the cost of chemicals involved can reach several thousands of dollars per kilogram. Further, contamination by-products that form are much harder to remove and can leave solid residue on the seals of valves and other components downstream of the container leading to component failure, and possibly to serious health and costly down time risks.
To improve the purging operation during container change-outs, better manifolds have been designed over the years (for example, see U.S. Pat. Nos. 5,590,695 and 5,964,254). However, even though better manifold design indeed leads to improved purging efficiency, operationally mishaps can occur from human error, computer controller errors, and component failures. Many compounds can lead to solid residues on valve seals, for example, which in turn leads to valve malfunctions. When such problems occur at chemical container filling locations, the degraded product will be detected in the routine product quality control procedures; however, when it occurs at a user""s site location the problem exhibits itself only after it causes down time and hazardous shut-down scenario.
An alternate means of preventing air contamination from entering the container is the use of breakseals (for example, see U.S. Pat. Nos. 4,134,514; 4,140,735; 4,298,037; 4,851,821; 4,966,207; and 4,979,643). As indicated in many previous patents, use of breakseals is indeed quite common in the handling of air-sensitive compounds and does effectively prevent direct contact of air into the container. However, in the case of inefficient purge sequences, component failure, computer control problem or human error, such breakseals will not prevent air contaminants from entering the container.
In accordance with the present invention, containers for delivery of high purity reactive liquids using gaseous assist are presented, as well as methods of use of same. In one embodiment, the container comprises a container body, the container body having fluidly connected thereto a gas inlet and a reactive liquid outlet, the gas inlet fitted with a means adapted to hold a gas filter media, preferably internally in the container, and a gas filter media positioned within the means adapted to hold a gas filter media, the gas inlet having a gas inlet valve, the liquid outlet having a liquid outlet valve. Preferred containers are those wherein the gas filter media is selected from a group consisting of silica, alumina, aluminosilicates; and containers wherein the liquid outlet is fitted with a means adapted to hold a liquid filter media, and a liquid filter media is positioned within the means adapted to hold a liquid filter media. Preferably, the liquid filter media is selected from a group consisting of silica, alumina, aluminosilicates. Other preferred containers are those wherein the means adapted to hold a gas filter media, and the gas filtered media, are integral to the container, and containers wherein the means adapted to hold a gas filter media comprises a conduit having a conduit inlet end positioned in said gas inlet of the container, the conduit having a conduit outlet end. Preferably, the conduit outlet end is internal to the container body. Preferably, the gas filter media is positioned between first and second gas filter media holders, both of the gas filter media holders being porous to gas used in gaseous assist delivery of liquid chemical adapted to be delivered from the container. Yet other preferred containers of the invention include those wherein the body has fluidly connected therewith a degas unit, the degas unit preferably integral with the liquid outlet and internal to the container body. Particularly preferred are containers of the invention wherein the reactive liquid does not make physical contact with the liquid filter media. This may be accomplished by use of means such as check valves, fine porous filter media, or even an elongated or coiled tube, as discussed herein. Also, the gaseous and liquid filter media may be external to the container in certain embodiments, positioned in close proximity to the container top.
Another aspect of the invention is a method of delivery of a high purity reactive liquid chemical to a point of use using gaseous assist, the method comprising the steps of:
(a) connecting the gas inlet of the inventive container to a source of gas, the container having liquid chemical therein;
(b) connecting the liquid outlet of the container to means able to accept the liquid chemical;
(c) initiating flow of gas by opening the gas inlet valve; and
(d) preventing impurities from entering the container through the gas inlet means. Preferred methods of the invention are those including preventing impurities from leaving the container through the liquid outlet, preferably methods wherein step (d) comprises passing the gas through the gas filter media, the gas filter media selected from a group consisting of silica, alumina, aluminosilicates, and the like. Still other preferred methods are those wherein the step of preventing impurities from leaving the container comprises passing the liquid chemical through a liquid filter media, the liquid filter media preferably selected from the same group of filter media that the gas filter media is selected from.
A second method embodiment of delivery of a high purity reactive liquid chemical to a point of use using gaseous assist comprises the steps of:
(a) connecting the gas inlet of the inventive container to a source of gas, the container having liquid chemical therein;
(b) connecting the liquid outlet of the container to means able to accept the liquid chemical;
(c) initiating flow of gas by opening the gas inlet valve;
(d) preventing impurities from entering the container through the gas inlet means; and
(e) degassing the liquid chemical before the liquid chemical exits the container. Preferred methods within this aspect of the invention are those wherein the method includes preventing impurities from leaving the container through the liquid outlet; methods wherein step (d) comprises passing the gas through the gas filter media, the gas filter media selected from the group consisting of alumina, silica, and aluminosilicates; and methods wherein the step of preventing impurities from leaving the container comprises passing liquid chemical through a liquid filter media. Other preferred methods include those wherein the liquid filter media is selected from the group consisting of silica, alumina, and aluminosilicates.
As used herein, the term xe2x80x9cintegralxe2x80x9d means that a component is unable to be removed from the container body without great difficulty by an enduser. In this sense, xe2x80x9cintegralxe2x80x9d does not mean that the component cannot be moved at all, but merely that the component cannot be removed during the normal course of use of the container.
As used herein the term xe2x80x9chigh purityxe2x80x9d means that the liquid chemical is susceptible to contamination by contact with atmospheric air and its contaminants. Similarly, the term xe2x80x9creactivexe2x80x9d means that the liquid chemical may decompose upon contact with air and its contaminants.
Chemicals such as organometallic precursors used in chemical vapor deposition need to be delivered at higher pressure than that of their own vapor pressure. A non-comprehensive list of chemicals which may benefit from the invention are listed in Table 1. This is easily done by pressurizing the container with inert gas to force the liquid out of the container. However, in such operations, such liquid chemicals run the risk of being contaminated with air impurities. These impurities, particularly moisture, react with many organometallic compounds to form other hazardous materials from the container. To prevent this from occurring, the container of the present invention has a design with an appropriate purifier to remove atmospheric contaminants before entering the container in the event of residual air being present in connecting lines which was not removed due to improper purge from operator handling, computer controller errors, or equipment component failures. Thus, better safety of chemical storage and improved assurance of chemical purity is attained which is often needed for critical processes such as that in the semiconductor industry. A particularly preferred method in accordance with the invention of preventing air contaminants from entering the container of the invention is to incorporate a purifying medium integral to the container itself and downstream of any line fittings that are disconnected for container change-outs. In accordance with the present invention, such purifier is preferably placed inside the container on the gas inlet port. Alternatively, such purifiers can be installed on both gas inlet and liquid outlet ports of the container. By making them an integral part of the container, no operator maintenance or intervention is required and the user is guaranteed the appropriate size and media to use for a particular chemical.
Thus, by incorporating a purifier on the gas inlet port of the container the inert gas used to pressurize the container will not contribute contaminants to the chemical. By making such purifier an integral part of the container, rather than fastening the purifier to the gas inlet line exterior to the container, there is far more certainty that all gas entering the container goes through the purifying media, thereby more effectively preventing error of contamination. Furthermore, preferably changing the filter media with every container change prevents over use of the filter media, and a human operator does not have to closely track usage of the filter media. The filter media is preferably economically sized for just one container volume of chemical, and preferably the filter media can be regenerated for use with another container.
As far as known to the inventor, no such container is available which incorporates purifiers directly into the container itself. Further, while it may be obvious that using gas purifies upstream of the gas flow can help assure purity of the gas itself, today, gas purity is rarely the problem since very high purities are usually attainable and commercially available. More frequently, the difficulty is in providing the user of liquid chemicals the assurance of reliable operations in purging out air contaminants sufficiently that result from installing new or replacement container by chemical delivery system.
The invention will be better understood with reference to the drawing figures and description of preferred embodiments which follows.